DMC/2 ignition for 750 SF3 – where's the codeswitch?

[JulianE]

Delighted to report that I finally got out for 20 miles on the Weston super Mare road this morning to assess new timing. I decided to put it on number 10 on the Witt box to start with, as piranha-bro2 suggested.

What a huge difference!! Much smoother curve, 90 percent less vibration, a pleasure instead of, frankly, a pain to open her up. Not perfect but having run pretty smoothly up to 75mph, I could see it from there.

When I have time, will go back to basics with a dial gauge and strobe it (what time of day is good to run her at 5000rpm on my driveway?). For now it’s much, much more than good enough. Will be finding a decent sized ride for tomorrow.

Grazie a tutti for your help!
Julian

 

[piranha-bro2]

Good news, Julian. It'll never be turbine smooth, but well set up they are very easy to live with. Are you familiar with using a piston stop to find absolute TDC? A dial gauge haS too much margin for error.

Pretty simple - make a 'stop' out of an old spark plug. Fit a degree wheel to the crank and rotate the engine away from TDC (on compression stroke to avoid valves hitting your stop). Fit the stop, rotate crank gently until the piston 'stops', note the pos on the degree wheel, rotate in the opposite direction and gently bring the piston up to the stop, note the pos on the degree wheel: TDC is exactly halfway between these two figures, eg if the total degrees between your two figures is 130, TDC will be 65 degrees from either side. Remove the stop, rotate the crank by that (eg 65) figure, set your pointer to zero - I always refit the stop and check just to be sure.

Then strobe away to your heart's content.

 

[JulianE]

Good news, Julian. It'll never be turbine smooth, but well set up they are very easy to live with. Are you familiar with using a piston stop to find absolute TDC? A dial gauge haS too much margin for error.

Pretty simple - make a 'stop' out of an old spark plug. Fit a degree wheel to the crank and rotate the engine away from TDC (on compression stroke to avoid valves hitting your stop). Fit the stop, rotate crank gently until the piston 'stops', note the pos on the degree wheel, rotate in the opposite direction and gently bring the piston up to the stop, note the pos on the degree wheel: TDC is exactly halfway between these two figures, eg if the total degrees between your two figures is 130, TDC will be 65 degrees from either side. Remove the stop, rotate the crank by that (eg 65) figure, set your pointer to zero - I always refit the stop and check just to be sure.

Then strobe away to your heart's content.

Possibly the best description of how to find TDC I've read. Although after watching a couple of videos about making a stop from an old plug, I took the non-serious mechanic's way out and just bought one (from feked.com).

Agreed not turbine smooth, but the relaxed pulling power from 2000 onwards is decidedly pleasant, and it's no slouch. Thanks again.

 

[stevepm2011]

And if after all that, it still vibrates inordinately, either you're not used to vibration or your crank isn't at 360°
Paul

Paul,
I admire your command of the English language! I haven't heard the word "inordinately" since I left boarding school. If I remember correctly, it was probably used immediately prior to me being caned (again)!
regards,
Steve

 

[Paul Marx]

Paul,
I admire your command of the English language! I haven't heard the word "inordinately" since I left boarding school. If I remember correctly, it was probably used immediately prior to me being caned (again)!
regards,
Steve

That's because I'm a part foreigner and have been out of the UK since before you were caned.
Vocabulary gets partly lost with time, the rest stagnates.
My mastery of English is shrinking faster than I am.
Paul

 

[iis_iis]

Notwithstanding the age will prevail in what was once instinctive recall, now declines into struggle and the dimming true meaning of words, all the while, opposed to the modern typical of shallow linguistic interpretations... I point the bone at "Contra-bute" UK mob, tsk.... or the Government report with "Morphology" as a repeated nonsense invented word, only a highly paid and under educated consultant could implement and remain clueless, i quipped, "do you own an Oxford Press dictionary" the answer was obvious and not sort upon my departure.

Mr M does have a command of the written word, over these many years.

My contribution to the topic proper, carburettor balance, triple and twin carbs, at 3000 to 3300rpm, balance at idle has no merit whatsoever. j

OP quote

What a huge difference!! Much smoother curve, 90 percent less vibration, a pleasure instead of, frankly, a pain to open her up. Not perfect but having run pretty smoothly up to 75mph, I could see it from there.